1. Field of the Invention
The present invention relates to a lens device, and more particularly to a lens device mounted in the camera body of a television camera.
2. Description of the Related Art
In a lens device mounted in the camera body of a television camera, aberrational variations such as spherical aberration, field curvature or coma aberration must be satisfactorily corrected. Thus, there has been proposed a floating imaging lens in which the lens system is divided into a plurality of groups, and each lens group is moved along the optical axis at a different velocity from each other when focusing is performed to correct the aberration, whereby satisfactory optical performance is maintained in focusing the lens on a short distance object. For example, Japanese Patent Application Laid-Open No. 2006-64972 has proposed a two-group floating lens device capable of satisfactorily correcting aberrational variations, in which-two lens groups are moved a different amount from each other.
By the way, as the drive mechanism for moving two lens groups at different velocities, for example, a cam mechanism described in Japanese Patent Application Laid-Open No. 2000-232603 can be used. More specifically, cam pins are arranged in a protruding manner on the outer circumferential surface of lens frames that hold respective lens groups, and these cam pins are each made to penetrate through a straight groove of a fixed cylinder and at the same time to engage with a plurality of cam grooves of the cam cylinder. According to this cam mechanism, when the cam cylinder is rotated, each cam pin moves along the respective cam grooves, so each lens group can move longitudinally in a direction of the optical axis.
However, when the above described cam mechanism is used as the floating system, the plurality of cam pins arranged in the respective lens frames are disposed at a distance from each other in a direction of the optical axis, resulting in a problem that the cam cylinder in which the plurality of cam grooves are formed is extended in a direction of the optical axis and thus the size of the device becomes large. Consequently, in the case of the lens device having a limited length in a direction of the optical axis, the cam mechanism cannot to be used as the floating system having plural lens groups.
The present invention has been devised in view of these circumstances, and an object thereof is to provide a floating lens device capable of moving a plurality of lens groups by a different amount, wherein the lens device can be miniaturized in a direction of the optical axis.